Human color sensitivity...

[Rastermon2]

From various studies I've seen, the human eye sees best, or responds most to the frequencies of green. It may have been discussed before, but I would guess that is a result of a selection preference to determining different kinds of plants - what's poisonous and what's not.

Also, designers know that blue falls to the background. But do they know it's for the same reason the sky is blue? The farther something is, the more blue light is scattered. our eyes and brain have adapted to to our environment.

[Delvo]

I don't know of a reason why we would be most sensitive to green. I'm not even sure what that description means. The only specific interpretations I know of for "most sensitive/responsive" are actually statements that would be true of blue or red instead.

In very dim light, our blue receptors are the last cones to still be able to respond when the red- and green-receiving cones are receiving too little light for them to detect. That's why natural light at night seems blue (even though you get most vision in the "dark" from rods, not cones), which in turn is why all human cultures associate blue with calmness, stillness, coolness, and relaxation. When artists talk about blue being a "background" color, they mean it in an emotional sense, not a geometrical one. It's not that we see blue and think it's far away, but that we see blue and think of the blue thing we're seeing as somehow subdued, quiet, mellow, inactive, not likely to be the driving force in the scene.

And our red receptors are the ones that get our attention the most and enable the greatest degree of distinction of different shades and hues in their part of the spectrum. In nature, they'd ordinarily only be strongly stimulated by certain things which only make up a small fraction of our general experience but really should be noticed and responded to, like blood, fire, poisonous animals, and ripe fruit or flowers. (Some would add the blood flow status of fellow members of one's own species, since that can reveal moods or health or reproductive readiness, but the first two only work if your species isn't furry, which our ancestors still were when the red receptor appeared, and the third only works if your species makes a physiological display of reproductive readiness, which humans don't.) That's why all human cultures associate red with action, intensity, brightness, and warmth, and all human languages have more basic color words for colors that strongly stimulate our red receptors than for colors that don't.

With blue and red as emotional opposites and at opposite ends of the color spectrum, green tends to get trapped in the middle (although closer to blue), not generally considered especially hot or especially cold, for example. And its technical factors, such as the shape of the response curve for the green-receiving cones in our eyes, also don't particularly stand out as the most or least in any way that I know of. And, for plant identification, sizes and shapes (and smells, for other species) are more useful than the shade/hue of green in the leaves.

I want to know where the idea of green as the most or least of anything came from. Could the sources you're talking about have been talking about the sun producing marginally more green light than other colors (which I'd expect to have the opposite effect, giving animals on this planet less of a need to be sensitive to it)? Could they have been talking about night-vision equipment which displays/records a scene in green monochrome? Could they have been referring to why the early computer monitors were often green monochrome?

[Cougar]

...green tends to get trapped in the middle...

Maybe that has something to do with it - green being in the middle of the visible part of the spectrum... ROYGBIV

[grant hutchison]

I don't know of a reason why we would be most sensitive to green. I'm not even sure what that description means.

Watt for watt, you get the greatest perception of brightness in the green range of the spectrum. It's called the luminous efficiency function, measured in lumens per watt. The function is roughly bell-shaped, with a central peak in the green and two tails into the red and violet.
The advent of cheap green lasers has meant that laser pointers recently shifted from red to green for exactly this reason: you get a brighter spot on the screen for the same battery life, or the same brightness with longer battery life.

Grant Hutchison

[Perikles]

Maybe that has something to do with it - green being in the middle of the visible part of the spectrum... ROYGBIV

Would this be the place to ask whether anybody can give an explanation for Aristotle's description of the rainbow as having three colours only?

Meteorologica 374b32ff

When the sight is fairly strong the colour changes to red, when it is less strong to green, and when it is weaker still, to blue. There is no further change of colour, the complete process consisting, like most others, of three stages; any further change is imperceptible. This is why the rainbow is three-coloured, and why, when there are two of them, each is three-coloured, but the colours are in the reverse order in each ...

Aristotle was (usually) extremely observant to detail (e.g. above, the reversing of colours in the second rainbow) but it is a mystery to me why he only saw three colours.

[grant hutchison]

Would this be the place to ask whether anybody can give an explanation for Aristotle's description of the rainbow as having three colours only?

Classical Greek colour terms are weirdly complicated and so difficult to parse that, as John Lyons reports, there has been some more-or-less-serious discussion as to whether the Greeks of that era were colour-blind! According to Lyons, the colour names seem to be strongly connected to brightness and texture, as well as hue.
Perhaps the luminous and textureless nature of a rainbow restricted Aristotle to only three colour names?
Which of the several word for red, green and blue did he use, by the way?

Grant Hutchison

[kleindoofy]

Classical Greek colour terms are weirdly complicated ...

It's not just the Greeks.

Color perception, groupings, etc. vary widely from culture to culture, especially green-yellow and red-blue. While we all see the same colors, we group and compare them differently.

When I first moved to Austria in 1976, at least in Salzburg they didn't use a seperate word for orange, they just called it red.

Some ancient texts refer to Lapis Lazuli as being red while we call it blue.

etc. etc.

There's an interesting little experiment. Take a little of the liquid out of a jar/can of conserved blueberries. It's blue. Now drop a spoonfull of it into a bowl of water. It turns red.

Go to a printing shop and have a look at the inks they use. The yellow for CMYK looks very greenish in the can, only to turn bright yellow when spread out thinly. The magenta looks almost blue and the cyan kind of blueish red.

[grant hutchison]

It's not just the Greeks.

Color perception, groupings, etc. vary widely from culture to culture, especially green-yellow and red-blue.

Other examples are the green-blue-grey-brown continuum in Gaelic and Welsh, and the Russian insistence that dark blue and light blue are different colours.
But as I say, the ancient Greeks seemed to have something else going on apart from the usual variations in how different languages split and name the colour continuum. It might all make more sense if we could speak to them about it, show them a couple of test chips ... But we're stuck with trying to decode the context of the writing.

Grant Hutchison

[Perikles]

Which of the several word for red, green and blue did he use, by the way?

Grant Hutchison

φοινίκος - red;
πράσινος - green;
άλουργον - blue (or purple, from άλς + έργον, wrought by the sea)

Could you give me a reference to the discussion about colour blindness with the Greeks? I was beginning to come to this conclusion myself.

[grant hutchison]

φοινίκος - red;
πράσινος - green;
άλουργον - blue (or purple, from άλς + έργον, wrought by the sea)

I wonder if these might not be seen as spanning red+orange, yellow+green and blue+violet, in English colour terms.

Could you give me a reference to the discussion about colour blindness with the Greeks? I was beginning to come to this conclusion myself.

I take it from the chapter by John Lyons in the book Colour Art & Science, edited by Trevor Lamb and Janine Bourriau (1995).

Scholars have long been aware of problems attached to the translation of particular colour-terms in the Classical languages. They have argued about whether Latin purpureus meant 'red' or 'purple' or something different; they have wondered what shade of blue the Latin word caeruleus denotes and whether it could ever mean 'blue-eyed'; they have puzzled over the true meaning of glaukos (which was used most famously, of course, of the eyes of Athene); more generally, they have noted the impossibility of translating the colour-terms of Greek and, to a lesser extent, Latin consistently and systematically into English, French, German or any modern European language. So acute is this problem that some scholars have seriously considered whether the ancient Greeks were colour-blind.

Grant Hutchison

[tdvance]

The Earth's atmosphere is the most transparent to a few ranges of frequencies of light, including what we call the visible spectrum (with some near infrared and ultraviolet as well), and some radio frequencies (enabling communications satelites). Given that eyes the size of satellite dishes just to see one pixel are a bit impractical, we evolved eyes to see what we consider the visible range, which has green roughly in the middle (on the logarithmic scale).

I'm not sure if there's a reason plants are green (I think there are purple photosynthetic substances that some archaeabacteria use). It could be that a convenient, easy-to-produce, efficient substance just happened to be green.

[kleindoofy]

... I'm not sure if there's a reason plants are green ...

Which brings us to the inevitable question as to whether matter which does not emit light acutally *has* a color or just absorbs resp. reflects certain wavelengths.

That may just be semantics, but it's worth mentioning.

[TrAI]

Which brings us to the inevitable question as to whether matter which does not emit light acutally *has* a color or just absorbs resp. reflects certain wavelengths.

That may just be semantics, but it's worth mentioning.

Well, they do not, nothing has color, either reflective or emitting objects, color is a way for our optic system to represent the information that certain parts of the imaged scene has more or less of certain frequencies to the our consiousness. They may emitt or reflect certain frequencies, but color only exists inside our minds.

It is similar to how we may choose to use a false color map or some mapping that brings out certain features in an image, the frequencies that this map uses is irrelevant to the operator as long as it does its job, and these representations do not have to conform to the actual nature of the imaged objects, you could actually represent the data to some other sense with the right equipment..

[Delvo]

About the rainbow subdivisions... since it's actually a continuous spectrum, any observer can break it up into as many or as few pieces as (s)he likes, so he wasn't wrong; notice that our own culture has two different systems for the same thing: the 6-color one most of us live by in all other contexts, and the ROYGBIV menmonic device which insists that "indigo" is a separate color from blue and violet even though none of us would ever count it as such in any other context. Neither of those two is exactly right or wrong either, one of them just doesn't fit the usual pattern for our culture. So Aristotle was free to correctly use any number he wanted.

Notice that Aristotle said, in that quote above, that the process which determines the rainbow's colors consists, "like most others", of three parts. So maybe Aristotle was just using the number 3 because he already believed that number to be an important universal principle, because he also had a list of other phenomena which split into three parts and took this opportunity to includes rainbows in the list. Also, I can kindo see a three-part division myself, not in terms of spectral colors, but in terms of brightness or contrast compared to the surrounding colors, with the yellow area down the middle appearing brighter or standing out more than the two less-brilliant sides.

Several other people at another forum told me a while ago that ancient Greek physical descriptions of gods and heroes had a tendency to say they had blond hair. I found this hard to believe because most Greek people back then would never see blond hair in their lives, and if they did it would be on a northern barbarian so they wouldn't think of it as a good and heroic thing. I thought it must be a translation issue, such as that they had no word for true blond so when they tried to describe it in those foreigners they could only use the lightest hair color word they did have, thus causing some translators to think that word always meant blond whereas in fact it normally just meant the lightest shade the Greeks themselves had and might actually envision their heroes having (still brown instead of actually blond, but just not black).

[Delvo]

Given that eyes the size of satellite dishes just to see one pixel are a bit impractical, we evolved eyes to see what we consider the visible range, which has green roughly in the middle (on the logarithmic scale).

The range we call visible (and some IR & UV) is not only a range that air is transparent to, but also between two extremes in terms of energy level and interaction with the matter they hit. Lower energy levels tend to have too little effect on most substances, and higher energy levels tend to be ionizing & destructive. Optical pigments need to be able to absorb just enough energy to provoke some kind of structural or chemical change but leave the molecules generally intact.

I'm not sure if there's a reason plants are green (I think there are purple photosynthetic substances that some archaeabacteria use).

There are a variety of red, purple, blue, and yellow/organge pigments used by bacteria, algae, and vascular plants. They're what you're seeing in the leaves that change colors in autumn, because not all pigments break down or get extracted from the leaves at the sate rate. They're also part of the reason why different species have slightly different shades of green. I've seen some people assert that it would be better not to use green pigments because they absorb mostly red, the least-energetic color, and red would be better because it absorbs more energetic blue & purple light, but the fact that plants DO produce those other colors proves they CAN, which means the predominance of green has to be due to its normally being the most useful one in their collection of pigments.

It could be that a convenient, easy-to-produce, efficient substance just happened to be green.

Those kinds of factors can influence which of several pigments is the most useful one; another that comes to my mind is molecule reusability & longevity.

Watt for watt, you get the greatest perception of brightness in the green range of the spectrum. It's called the luminous efficiency function, measured in lumens per watt.

Intersting... I recall an encyclopedia article showing what color it said was perceived as the brightest, and it was a certain shade of orange, I think essentially the peak frequency of our red-receptors' response curves (because of how stimulation of that type of cone stands out and gets our attention). But that was on paper and described tests that had been done on paper or other such dyed/pigmented/painted swatches, not electronics (the encyclopedia having been published in 1957), so it probably wasn't in terms of wattage.

[mugaliens]

Actually, bluish-green is one of the more difficult series of shades for the human eye to differentiate, due to the frequency response curves of our S, M, and L cones leaving quite a gap centered around 485 nm.

Unless you're a tetrachromat. Then again, one study says the fourth human cone lies between the red and the green, not the green and the blue.

Ah, what do they know?

[Perikles]

Notice that Aristotle said, in that quote above, that the process which determines the rainbow's colors consists, "like most others", of three parts. So maybe Aristotle was just using the number 3 because he already believed that number to be an important universal principle.

Yes, point taken, the number 3 always had some overpowering universal principle attached to it. I can see the grouping of red and orange, and the grouping of blue and purple, but I have difficulty in accepting that yellow and green can have the same name.

Several other people at another forum told me a while ago that ancient Greek physical descriptions of gods and heroes had a tendency to say they had blond hair. I found this hard to believe because most Greek people back then would never see blond hair in their lives.

Amongst other puzzling words, this is probably the vexing issue of exactly what the Greek word xanthos might mean, traditionally translated as blond. First, though, I think a general label of 'ancient Greeks' is misleading - they were a wide variety of city-states over a large area and could include Mycanean Greeks of 1200 B.C as well as Alexandrian Greeks of up to 100 B.C. (Alexander himself was a Macedonian). There is plenty of opportunity for different racial types amongst this mix, and I wonder why you think there was no opportunity to see blond hair. Second, even the word blond has different meanings even in modern European cultures: I am described as blond (rubio) by my Spanish neighbours, and what is left of my hair would be described as dark brown in the UK.

Vernant:

xanthos means blond in the sense of gilded, suggesting brilliance that describes gold and fire. Xanthos is different from chloros (yellow-green), which connotes paleness, even weakness. (Fear, deos, is called chloron).

I could drone on about this, but the short response is that there is little reason to argue that the Greeks only ever saw black hair. I can't imagine a golden Aphrodite as having anything other than blond(-ish) hair, and this epithet for her is so universal that it is difficult to argue against.

[Delvo]

I can see the grouping of red and orange, and the grouping of blue and purple, but I have difficulty in accepting that yellow and green can have the same name.

It would be more common for the span from red to yellow to be two of categories (the ones that stimulate our red receptors, separated according to how much they do so), with the span from green to purple being the third (the ones that practically stimulate our red receptors at all). I get this from linguistics, not optics, although I took a lesson in perceptual optics from it. Not all languages have the same number of basic, top-level, broadly categorical color words (things like green and purple, not more specific ones like vermillion and chartreuse), but all languages that have the same number have the same conceptual set; they don't divide the spectrum up in randomly different ways that just happen to end up with the same number...

0. At the starting point there are always two words which could be translated as "white" and "black" or "bright" and "dark", but sometimes there are no words with the exclusive job of indicating a color's place in the EM spectrum. The speakers of such languages are more likely to place, for example, red swatches in the former category and blue ones in the latter, bu tnot necessarily, especially with dark red and bright blue. The two words also pull double-duty as metaphors for heat and cold, or intense moods versus calmness. After this point, I'll only be addressing the addition of words that specify only a color's place in the spectrum and nothing else about it, excluding the points at which we also got gray (neutral color, no position on the spectrum), pink (specifies not just spectral position but also saturation or purity), or brown (specifies not just spectral position but also brightness/darkness).

1. The third word in three-word langauges, and the first to specify a color's position on the spectrum, is always something that tends to get translated as "red", but also gets applied by the natives to things we'd call orange or yellow. (Essentially, it's anything that strongly stimulates our red receptors, although my linguistics professor & book didn't note that.) Because it distinguishes things that might otherwise be together under the "bright" category in a two-color language (separating red from white, to be the most basic about it), it's said to "split off" from that word or its concept.

2. The next word in languages with just one more word is always simply the other half of the spectrum, green through purple; it's split off from the "dark" category.

3. After that, as evolving languages add or subtract color words, they simply alternate for a while between these two groups, splitting off one more at a time. So with 3, two of them are what we'd call red and yellow, plus the inclusion of what we'd call orange, most of which go into the "yellow" category, which some linguists call "orellow". The green-to-purple half of the spectrum remains just one basic word, which some linguists call "grue". This is the linguistic evolutionary point at which you'd essentially have no choice but to say a rainbow has three colors (red, orellow, and grue), which is why I'd expect it to also be the most likely three-way categorization even for people with other words available.

4. It's grue's turn to split next, splitting off green (or green and some of blue's territory); purple and (all or the remainder of) blue are still shades of one basic thing.

5. The next split is orange becoming distinct from red and yellow.

6. The next split is purple becoming distinct from blue.

7. There are other color words that get added later, but, other than ROYGBIV (and even our own culture doesn't really categorize colors like that, since "indigo" isn't used that way in any other context), I don't know of any that divide the spectrum into 7 pieces in order, instead of basing definitions on both spectral position and something else, like pink and brown do.

Amongst other puzzling words, this is probably the vexing issue of exactly what the Greek word xanthos might mean, traditionally translated as blond... I could drone on about this, but the short response is that there is little reason to argue that the Greeks only ever saw black hair.

I didn't say only black; I said not blond, or at least not except for on foreign barbarians, which they did not generally look up to and idolize, so it would be odd to describe fictional heroes as looking like them. My solution to this was that the word we're now translating as "blond" didn't mean white or yellow as the modern English word "blond" is generally used (things too light to be called brown), but could have meant just "lighter than usual", which for the Greeks would still be brown, not white or yellow, making "blond" a bit of a mistranslation for it even if they did also use it for truly white/yellow hair too.

[Perikles]

My solution to this was that the word we're now translating as "blond" didn't mean white or yellow as the modern English word "blond" is generally used (things too light to be called brown), but could have meant just "lighter than usual", which for the Greeks would still be brown, not white or yellow, making "blond" a bit of a mistranslation for it even if they did also use it for truly white/yellow hair too.

Yes, I would agree that xanthos is badly translated as blond, and must cover a much wider colour range. In the Iliad, for example, the adjective is applied to Achilles' hair; Menelaus; Demeter; Agamede; and some horses heads. There is also the river 'who is called Xanthos by the Gods, but by mortals Skamandros'.

Significantly, in the Homeric Hymn to Demeter, the goddess has the epithet xanthe. She had an intimate connection with fertility, especially corn, and so in this instance, xanthe very likely means corn-coloured hair.

The epithets relating to colour in Greek epic should of course be understood in the context that the rigid constraints on rythym and metre severely restrict the use of vocabulary. Thus nouns can only have adjectives describing them which fit in, and perhaps accuracy of description is lost to the benefit of poetry.

As for Aristotle's three rainbow colours, he muddies the waters by continuing with an attempt at explaining why there is a yellow (xanthos) between the red and the green (375a6ff). The argument here is difficult to follow, but his identification of xanthos as lying between red and green clearly shows that it can mean yellow (-ish).

[Delvo]

She had an intimate connection with fertility, especially corn, and so in this instance, xanthe very likely means corn-coloured hair.

And speaking of word changes... what we now call "corn" is maize, a North American plant. Perhaps the translation you're talking about was translation into an earlier-than-present version of English, in which corn meant any grain such as wheat or rye or oats... or even salt, because it comes in little grain-size pieces, which is why salted meat is still called "corned" meat.

[Perikles]

And speaking of word changes... what we now call "corn" is maize, a North American plant. Perhaps the translation you're talking about was translation into an earlier-than-present version of English, in which corn meant any grain such as wheat or rye or oats... or even salt, because it comes in little grain-size pieces, which is why salted meat is still called "corned" meat.

Well, yes, I was referring to what the Greeks would identify as a normal yellowish grain crop, without committing myself. Probably wheat or barley. This is not an earlier-than-present version of English, just modern English, in England.

[kleindoofy]

... I have difficulty in accepting that yellow and green can have the same name. ...

The Babylonians had a word (which I would have to go look up) which is usually translated as "yellow-green" and was used to describe the color of half-ripe wheat/barley/rye plants. It was also used to describe the color of somebody's face when they became distressed, e.g. "her [the godess'] face turned yellow-green" used for Inanna when facing death in the "Inanna and Dumuzi" myth.

Some word pairs for colors follow the shades things become when ripening: red-blue (berries), green-yellow (wheat), etc.

Perceiving and grouping colors doesn't follow any one set pattern across cultural lines and can correspond to a logic that is blatantly obvious to one group while invisible to another.

... I am described as blond (rubio) by my Spanish neighbours, and what is left of my hair would be described as dark brown in the UK ...

Modern German uses "blond" for the very fair color which English depicts as blond, but also for the English brunette. Currently they are beginning to distinguish between "light blond" (hellblond) which corresponds to the English word and "dark blond" (dunkelblond) which equals brunette. However, when a woman is referred to as a "Blondine," it usually means she's light blond.

[Rastermon2]

This is what I meant by sensitivity to green light
-From Wikipedia